CRINOIDS Commonly called sea lilies. Like echinoids they show a 5-fold symmetry. They have an endoskeleton made of calcite plates. To some extent they are jointed to allow flexibility. Unlike echinoids they were sessile (mainly). They are gregarious. Modern crinoids live in a variety of water temperatures but fossil ones tended to live in warm waters. Common in limestones. Most lived in shallow shelf areas away from tides down to 200m.

Crinoid Morphology Draw Fig. 123 page 198 of Black. STEM Varies in length and consists of a number of plates called columnals or (ossicles). They are not rigidly fixed but could sway. The shape of each columnal varies between circular and star shaped (123 c draw). In the centre of the columnal is an axial canal which allowed part of the soft tissue to pass through. Some stems were anchored by a root like system called a holdfast.

Crinoid Morphology 2 Draw Fig123 e on page 198 Black. CALYX Cup like structure sitting on top of the stem. Consists of circles of different types of plates: 5 lower basals. 5 upper basals. In some there is an extra row called infrabasals. There are also radials and smaller inter-radials. At the top are other small plates called brachials which are the beginning of the arms.

Crinoid Morphology 3 TEGMEN Occurs on the upper oral surface of the calyx. Can be either a membrane of calcite plates or a rigid dome. The anus lies between two food grooves.

Crinoid Morphology 4 ARMS These are also called brachials. Made of calcite plates. Extend from calyx and can sway due to joints between radial plates and lowest brachial plates. Arms usually branch into 2 each time. Smaller branches called pinnules. There is a deep groove on inside of arm. Tube feet catch food and transfer it down the groove to the mouth with the help of wafting (say it properly!) cilia.

Crinoid Geological History Mid Cambrian to Present. 1 genera in Cambrian. Reach prime in Silurian, Devonian and Carboniferous. Declined at the Permian extinction. Recovered in Mesozoic. Most common in limestones preserved as short sections of the stem or individual columnals.